This invention relates to electromechanical transducers and more particularly to such transducers employing push rods for force coupling with integral stopping mechanisms.
There exists a great variety of transducers which are used to measure force and pressure in different environments. As such, gages or load cells of many different types are normally employed in conjunction with suitable mechanical force transmitting strutures to achieve such measurements.
An extremely popular type of gage utilizes the well known piezoresistive effect, which effect is exhibited by certain semiconductor material and basically affords a change in resistance according to the magnitude of an applied force. Such devices using the piezoresistive effect are basically extremely small due to the fact that the device can be fabricated by utilizing integrated circuit techniques.
As indicated, there are many different configurations showing the use of such transducers and associated gages. Reference may be had, for example, to an article entitled DEVELOPMENT AND APPLICATION OF HIGH TEMPERATURE ULTRAMINIATURE PRESSURE TRANSDUCERS by Anthony D. Kurtz and John Kicks which was presented at the ISA Silver Jubilee Conference in Philadelphia, Pennsylvania in October, 1970.
As such, a fairly common type of transducer is sometimes referred to as a cantilever beam transducer and such devices in conjunction with gages, are used to sense and provide an output indicative of force and torque. The deflection of the beam causes the gages, which are positioned on the beam, to exhibit a change in resistance proportional to the force applied to the beam.
As is the case in most transducers, the accuracy of the cantilever or a beam transducer in general, depends upon the limit of deflection within the elastic range of the beam material. The same comments are applicable to other beam type transducers as the simply supported beam or the so-called clamped-clamped beam.
In the event, such cantilever structures can also be extremely small and respond to extremely small forces or torques while providing highly reliable and accurate measurments.
An example of one type of beam transducer is shown in U.S. Pat. No. 3,461,416 issued on Aug. 12, 1969 to E. N. Kaufman and assigned to The Lockheed Aircraft Corporation.
Essentially, the transducer operates in conjunction with a diaphragm upon which a force is applied. The diaphragm is normally coupled to the beam by means of a rod or a cylinder, which acts as a force transmitter.
As indicated, such devices are extremely small and one must assure that the deflection of the beam due to the application of the applied force, is held within the elastic limits of the beam material. One must also assure that an excessive force will not destroy the structure by causing a fracture or an actual breakage of the beam. Techniques for controlling the amount of deflection of the beam are known in the art and are generally referred to as stops. Inherently, most stops provided by the prior art are in the nature of mechanical devices such as pins, bosses and so on and essentially, are operative to prevent the exceeding of the elastic limits of the beam, which essentially can cause a complete destruction of the transducer or a permanent deformation of the beam resulting in unreliable operation of the transducer. However, such stops are not suitable for use with deflections of the order of 0.001 or less; and hence are referred to as gross stops.
The problems depicted are difficult to solve due to the extremely small size of the components as well as the extremely small deflection ranges of the units.
In particular, a cantilever structure presents problems which are peculiar to the configuration and hence, providing a stop mechanism in such a configuration, while maintaining good accuracy, is of considerable concern.
It is therefore an object of the present invention to provide an improved beam transducer employing built-in stops which are capable of assuring that the elastic limits of the materials are not exceeded, while further assuring that the beam will not rupture or fracture when external high forces are applied thereto: with regard to the small deflections used herein.